1. Field of the Invention
The present invention relates to a reflecting board for a microstrip reflectarray antenna and, more particularly, to a reflecting board with variable slot size that can improve the design flexibilities of the reflecting board and reduce the sensitivity to the manufacturing tolerances of the microstrip reflectarray antenna.
2. Description of Related Art
To provide broad bandwidth for high frequency communication, a microstrip reflectarray antenna is often used to transmit and receive a high frequency signal. As shown in FIG. 1A, the microstrip reflectarray antenna comprises a disc 11 and a horn 12. In addition, plurality of antenna patches 14 are disposed on the upper surface 13 of the disc 11, and a metal grounding-layer (not shown) is disposed on the lower surface of the disc 11. The horn 12 is coupled to the disc 11 through a support 15 at a predetermined distance above the disc 11. Therefore, as the reflect-array antenna 1 receives a high-frequency signal coming from a distant terminal, the high-frequency signal is concentrated and reflected to the horn 12 by the antenna patches 14 on the disc 11, and this signal is then received by the horn 12. On the contrary, as the reflect-array antenna 1 transmits a high-frequency signal, the signal transmitted from the horn 12 is reflected by the antenna patch 14 on the disc 11, and send to a distant-terminal receiving device.
To improve the gain and the bandwidth of the reflect-array antenna 1, the patterns of the antenna patches 14 are usually different from each other. Besides, the patterns of the antenna patches 14 variably depend on their location on the disc 11. Generally speaking, the patterns of the antenna patches 14 are divided into three types.
1. As shown in FIG. 1B, plural antenna patches 141, 142, 143, 144 disposed on the upper surface 13 of the disc 11 have delay lines 145, 146, 147, 148 with different lengths, separately. The function of these delay lines is to adjust the phase difference of the high-frequency signal reflected by the disc 11. This signal also controls the main beam direction after reflection. Hence, the high-frequency signal reflected by the disc 11 can be gathered effectively in the horns, and therefore, the reflectarray antenna 1 can transmit and receive the high-frequency signal.
2. As shown in FIG. 1C, plural antenna patches 14 disposed on the upper surface 13 of disc 11 could have different rotation angles or different types of delay lines (i.e. straight delay line 161 and bent delay line 162). It is known that the gain and the bandwidth of the reflectarray antenna 1 having this kind of antenna patch 14 are improved. Besides, the reflected high-frequency signal can be gathered in the horn 12 effectively, and therefore, the reflectarray antenna 1 can transmit and receive the high-frequency signal.
3. As shown in FIG. 1D, the disc 11 may have two-layer structured antenna patches thereon (i.e. the first antenna patches and the second antenna patches). Besides, these two-layer structured antenna patches could have different sizes according to their positions on the surface 13 of the disc 11. It can be seen that the first antenna patches 171, 172, 173, 174 are disposed on the upper surface 13 of the disc 11 and the second antenna patches 175, 176, 177, 178 are disposed on the lower surface (not shown) of the disc 11. Moreover, the ratio of the size of the first antenna patch to the size of the corresponding second antenna patch is identical for each first antenna patch on the upper surface 13 of the disc 11. For example, the border-length of the first antenna patch could be 0.6 times of the border-length of the corresponding second antenna patch.
However, the entire performance of reflecting array antenna is easily affected by the size and arrangement of the patterns of the antenna patches due to the material properties of the disc (e.g. the dielectric constant). Hence, producing the design of the disc is very difficult. Besides, the size and the position of every antenna patch needs to be manufactured precisely, otherwise, the high-frequency signal cannot be reflected effectively by the disc, and the performance (e.g. gain, bandwidth, or efficiency) of the disc can not be improved.
Therefore, it is desirable to provide a reflecting board with variable slot size to increase the design flexibility of the reflecting board and reduce the effect of manufacturing error on the performance of the microstrip reflectarray antenna. In this way, the manufacture cost of the microstrip reflectarray antenna can be lessened and the manufacture yield of the reflecting board can be raised.